DNS settings tend to have a lag time.
Have you attempted to access the app from another device? (Say a smart phone that is operating on another network?) I've seen on several occasions where my local dns cache was causing issues which is why accessing it from another device may shine some light on your situation.
If you're making the dns changes from a windows based pc you can flush your dns cache which can sometimes resolve your issue.
1.) Right Click on CMD.exe (aka command prompt)
2.) Click on Run as Administrator.
3.) type: ipconfig /flushdns
4.) Press Enter key
But bear in mind dns changes can take a while to propagate.
